U.S. Pat. No. 6,344,290 discloses a fuel cell formed by alternately stacking multiple discoid cell plates and discoid separator plates. A fuel gas inlet hole and an air inlet hole are formed on a central part of each of the cell plates and the separator plates.
According to this fuel cell, two gases of the fuel gas and the air are supplied from the respective central parts of the cell plates and the separator plates, and are discharged from outer peripheral portions thereof. Therefore, it is not possible to collect unburned gas, and as a consequence, fuel utilization efficiency drops when gas flows fluctuate in a transient operating condition or the like. Moreover, unstable combustion at the peripheral portion brings about local thermal stress to the individual cells whereby the individual cells may be damaged.
As a fuel cell for resolving such a risk of damage, Japanese Patent Application Laid-open Publication No. 2004-207028 discloses a fuel cell with a stack-structured member housed in a casing. The stack-structured member includes multiple solid electrolyte fuel cell units that are stacked on one another with current collectors interposed therebetween. Each of the solid electrolyte fuel cell units is formed by joining an outer peripheral portion of a cell plate for holding a unit cell and an outer peripheral portion of a separator plate. Inlet holes for one of a fuel gas and air are provided on respective central parts of the cell plate and the separator plate, thereby forming a central gas passage. The casing is provided with a gas inlet opening and a gas outlet opening through which the other one of the fuel gas and the air is supplied.